1. Field of the Invention
The present invention relates to a solid-state imaging device and a method for manufacturing a solid-state imaging device, and more particularly it relates to a solid-state imaging device in which a single-layer electrically conductive electrode film is processed so as to form a charge transfer electrode, wherein a narrow interelectrode gap is flattened, with improved step coverage in a metal interconnect or metal light-shielding film formed thereon.
2. Background of the Invention
FIG. 8 and FIG. 9 of the accompanying drawings show a sequence of cross-section views illustrating the processes in manufacturing a solid-state imaging device that uses a conventional buried type photodiode as an photoelectric conversion section (refer to Japanese Unexamined Patent Publication (KOKAI) No.5-267638).
In the above-noted process, thermal diffusion is first used to form a first p-type well layer 502 and a second p-type well 503 onto an n-type semiconductor substrate 501, after which ion implantation of phosphorus is done to form a vertical charge transfer section 504. Boron is then ion implanted to form a channel stopping region 506 and a charge reading region 505 (FIG. 8(a)).
Next, the surface of the n-type semiconductor substrate is thermally oxidized to form a gate electrode film 507, after which, as shown in FIG. 8(b), low-pressure CVD is used to form a charge transfer electrode material film 508 on the gate electrode 507. Patterning is then done for forming the reading electrode.
Then, photoresist 509 is used as a mask in performing dry etching so as to form a charge transfer electrode 510. Next, the charge transfer electrode with the photoresist remaining is used as a mask in performing self-aligning ion implantation of phosphor, so as to form the n-type well 511 that will serve as the photodiode. When this is done, the film thickness of the photoresist 509 is made approximately 3 xcexcm, so that the phosphorus ions do not penetrate (FIG. 8(c)). 
Then, to form the buried type photodiode, the photoresist 509 is removed, after which boron is ion implanted with the charge transfer electrode 510 used as a mask, thereby forming a p+ type region 512.
While FIG. 8 and FIG. 9 show a cross-section view of a pixel in the processes of manufacturing a solid-state imaging device, the plan view of pattern arrangement is, for example, as shown in FIG. 10.
In FIG. 10, a the charge transfer electrode is made by processing a single-layer charge transfer electrode material, a photoelectric conversion section being formed as a region enclosed within the charge transfer electrode. The cross-section views of FIG. 8 and FIG. 9 are as seen along the cutting line A-Axe2x80x2 in FIG. 10.
Four charge transfer electrodes taken as a unit, with a pulses of different phases (("PHgr"1 to "PHgr"4) applied to each, and in order to perform charge transfer using these pulses, it is necessary to provide a region 614 that separates the charge transfer electrodes in the row direction.
FIG. 11 is a cross-section view along the cutting line B-Bxe2x80x2 shown in FIG. 10. A region 714 is formed which separates the charge transfer electrodes in the row direction, a metal light-shielding film 717 being formed thereon, with an intervening interlayer insulation film 716 therebetween, thereby preventing light from striking the vertical charge transfer section.
In the above-noted solid-state imaging device of the past, however, as shown in FIG. 12, because the region (interelectrode gap) that separates the charge transfer electrodes in the row direction is formed with a short distance of approximately 0.25 xcexcm to 0.50 xcexcm, porosity develops in the interlayer insulation film 816 formed thereover or locations of poor coverage occur, so that breaks 820 occur in the metal light-shielding film or metal interconnect formed thereover, thereby causing the problem of deterioration in either the light-blocking characteristics or the charge transfer characteristics.
One method that can be envisioned to prevent interconnect breakage is that of flattening the entire surface before providing the interconnects. When this is done, however, because the photoelectric conversion section as shown in FIG. 13 is also flattened, there is an increase in the height of the metal light-shielding film from the surface of the substrate, so that angularly incident light 921 enters the charge transfer region, leading to a deterioration in smear characteristics.
Accordingly, it is an object of the present invention to solve the above-noted problem in a convetional solid-state imaging device, by providing a solid-state imaging device wherein a charge transfer electrode is formed by etching a single-layer charge-transfer material film, this etching region being divided into a first region to be divided in the row direction and a second region on a photoelectric conversion section, the etching region of the first region being filled with an insulation film, so as to flatten only the top part of the vertical charge transfer section or the bottom part of a region formed of a metal wiring for applying a drive voltage to a charge transfer electrode, thereby achieving a solid-state imaging device with good formation of metal wirings, without a deterioration of the smear characteristics.
In order to achieve the above-noted object, the present invention has the following basic technical constitution.
Specifically, the first aspect of the present invention is a solid-state imaging device comprising: a photoelectric conversion section formed within a surface region of semiconductor layer of a first conductivity type; a charge transfer section of a second conductivity type formed adjacent to the photoelectric conversion section within the surface region of the semiconductor layer of the first conductivity type, which receives and transfers a signal charge generated by the photoelectric conversion section; a read-out section formed in the surface region of the semiconductor layer of the first conductivity type for reading the signal generated by said photoelectric conversion section to the charge transfer section; and a single-layer charge transfer electrode formed over the read-out section and the charge transfer section, with an intervening gate insulation film therebetween, a region that separates the charge transfer electrode is filled with an insulation film having a height that is equivalent to or less than that of the charge transfer electrode.
In the second aspect of the present invention, a silicide film is formed on the surface of the charge transfer electrode.
The first aspect of a method of the present invention is a method for manufacturing a solid-state imaging device, the solid-state imaging device comprising: a photoelectric conversion section formed within a surface region of semiconductor layer of a first conductivity type; a charge transfer section of a second conductivity type formed adjacent to the photoelectric conversion section within the surface region of the semiconductor layer of the first conductivity type, which receives and transfers a signal charge generated by the photoelectric conversion section; a read-out section formed in the surface region of the semiconductor layer of the first conductivity type for reading the signal generated by the photoelectric conversion section to the charge transfer section; and a single-layer charge transfer electrode formed over the read-out section and the charge transfer section, with an intervening gate insulation film therebetween, an insulation film separating mutually adjacent the charge transfer electrodes; and a light-shielding film provided on the insulation film, the method comprising: a first step of etching of a first region on an electrically conductive electrode material film on the gate insulation film so as to divide the electrically conductive electrode material film and form the charge transfer electrodes; a second step of forming an insulation film over an entire surface and filling the first region with the insulation film; a third step of removing said insulation film until at least the electrically conductive electrode material film is exposed; and a forth step of etching a second region on the electrically conductive electrode material film so as to form an aperture in the photoelectric conversion region.
In a second aspect of the method according to the present invention, the photoelectric conversion section is formed in a self-aligned manner with respect to the second region.
In a third aspect of the method according to the present invention, the fourth step includes a process of siliciding a surface of the electrically conductive electrode material film.
In a forth aspect of the method according to the present invention, the third step further includes processes of forming a high melting point metal film over an entire surface, after removing the insulation film until the electrically conductive electrode material film is exposed, and siliciding a surface of the electrically conductive electrode material film by thermal treatment, and removing the high melting point metal film that is not silicided.
In a fifth aspect of the method according to the present invention, the fourth step includes a processes of etching the electrically conductive electrode material film using a mask, and ion implantation of a first conductivity dopant and a second conductivity dopant, using the mask and the electrically conductive electrode material film or the electrically conductive electrode material film as a mask, so as to form the photoelectric conversion section.
In a sixth aspect of the method according to the present invention, the fourth step further includes a processes of etching said electrically conductive electrode material film using a mask, and ion implantation of a second conductivity dopant, using the mask and the electrically conductive electrode material film or the electrically conductive electrode material film as a mask, and ion implantation of a first conductivity dopant, within a surface of the second conductivity region, using the charge transfer electrode as a mask, in a self-aligning manner.
In a seventh aspect of the method according to the present invention, the forth step further includes a process of controlling an angle of incidence of ion implantation of the second conductivity dopant, so as to form a second conductivity region that encroaches under the charge transfer electrode, thereby forming the second conductivity region in a self-aligning manner.
In a eighth aspect of the method according to the present invention, the forth step further includes a process of controlling an angle of incidence of ion implantation of a first conductivity dopant, so as to form a first conductivity type semiconductor layer in a self-aligning manner and at a prescribed distance from an edge of the charge transfer electrode.
A nineth aspect of the method according to the present invention is, a method for manufacturing a solid-state imaging device, the solid-state imaging device comprising: a photoelectric conversion section formed within a surface region of semiconductor layer of a first conductivity type; a charge transfer section of a second conductivity type formed adjacent to the photoelectric conversion section within the surface region of the semiconductor layer of the first conductivity type, which receives and transfers a signal charge generated by the photoelectric conversion section; a read-out section formed in the surface region of the semiconductor layer of the first conductivity type for reading the signal generated by said photoelectric conversion section to the charge transfer section; and a single-layer charge transfer electrode formed over the read-out section and the charge transfer section, with an intervening gate insulation film therebetween, an insulation film separating mutually adjacent the charge transfer electrodes; and a light-shielding film provided on the insulation film, the method comprising: a first step of forming an electrically conductive electrode material film on the semiconductor layer of the first conductivity type, with the intervening gate electrode therebetween; a second step of forming a first mask on the electrically conductive electrode material film; a third step of etching a first region of the electrically conductive electrode material film, using the first mask, and dividing the electrically conductive electrode material film in a row direction; a fourth step of forming an insulation film over the entire surface; a fifth step of performing thermal flow of the insulation film; a sixth step of etching the insulation film so as to expose a surface of the electrically conductive electrode material film; a seventh step of forming a second mask over an entire surface; and an eighth step of etching a second region on the electrically conductive electrode material film, using the second mask, so as to form an aperture in the photoelectric conversion section.